Method of and apparatus for freezing water-bearing materials



March 12, 1968 c. E. SCHROEDER 3,372,550

METHOD OF AND APPARATUS FOR FREEZING WATER-BEARING MATERIALS Filed May 3, 1966 I N VEN TOR.

' c L E. sc/moeom BY ATTORNEY United States Patent 3,372,550 METHOD OF AND APPARATUS FOR FREEZING WATER-BEARING MATERIALS Carl E. Schroeder, 715 E. Liberty, Ponca City, Okla. 74601 Filed May 3, 1966, Ser. No. 547,296 Claims. (CI. 61-36) ABSTRACT OF THE DISCLOSURE Method and means are provided for freezing waterbearing material, such as earth, in zones such that the temperature decreases with depth. The lower temperature freezing at greater depth provides additional structural strength at the point of need.

Disclosure This invention relates to a method of and apparatus for freezing earth and other water-bearing materials. More particularly, this invention relates to a method of and apparatus for minimizing the refrigeration requirements for freezing water-bearing materials prior to the removal of adjoining materials, such as earth.

In present construction procedures, it is often found desirable to freeze a portion of water bearing material, such as soil, prior to the removal of adjacent material. For instance, in locations where there is abundant ground water which would otherwise encroach into an excavation, one technique commonly employed is to surround the proposed excavation site with a plurality of freeze points and I to circulate low-temperature materials in the freeze points to form a wall of interstitial ice completely surrounding the excavation site. By this means encroachment of the ground water during excavation is prevented. In addition, the structural competency of the water-containing formation is enhanced due to the presence of the interstitial ice. As would be expected, the required strength of the ice increases with the depth of the adjacent excavation. That is, near the top of the excavation only minimum horizontal pressures are encountered due to the overburden and to the ground water head; however, as the excavation progresses downwardly, not only does overburden pressure increase but static hydraulic head acting on the ground water likewise increases. These increased horizontal pressures require increased strength in the wall of the ice if the desired function of the ice wall is to be realized.

Until the present invention it has been common practice to circulate low-temperature fluids throughout the vertical length of the freeze points until the strength of the ice along substantially the entire length of the freeze point is adequate to withstand the pressures that will be encountered only at the bottom of the excavation. Manifestly, such techniques result in a waste of refrigeration since the upper portions of the earth are frozen to a degree not necessitated by any engineering consideration.

In attempting to minimize the refrigeration capacity requirement under these circumstances there are two factors which should be kept in mind. First, and most obvious, in general the thicker the ice the greater the strength. Second, and in the present application most important, the colder the ice, up to a point, the greater its strength. With these factors in mind, it has been discovered that by utilizing thermally-zoned freeze points it is possible to obtain relatively high strength adjacent the lower portions of the freeze points while maintaining adequate strength at the upper portions thereof without over refrigerating such upper portions; however, until the present invention, a freeze point capable of producing adequate strength in an ice wall surrounding an excavation without v ice utilizing excess refrigerating capacity had remained an elusive desideratum.

It is, therefore, an object of the present invention to provide an improved method of and apparatus for freezing water bearing material.

Another object of this invention is to provide a method of and apparatus for freezing water bearing material to provide adequate structural strength for later excavation adjacent the frozen portion of the water bearing material with a minimum refrigeration requirement.

A further object of this invention is to provide a freeze point capable of producing a vertical thermal gradient immediately adjacent the surface of the freeze point.

Yet another object of the present invention is to provide a method of and apparatus for forming an ice wall having greater strength at the bottom than at the top thereof.

Other objects of this invention will become apparent from the following description and associated drawings wherein at least one method and apparatus for practicing the present invention are described.

In one aspect, the method of the present invention may be described as comprising the steps of forming a hole in the earth, dividing said hole into a plurality of chambers and placing a first low-temperature material in the uppermost chamber. Either simultaneously or subsequently the lower chamber or chambers have placed therein other low-temperature materials, the temperature of which is lower than that of the material in the upper chamber and which, when more than two chambers are provided, decreases with each subsequently lower chamber.

In one aspect, apparatus embodying the present invention may be broadly summarized as comprising a bore hole formed in the earth which is divided into a plurality of vertically spaced chambers. Means are provided for isolating these chambers and additional means are provided for allowing communication between the surface of the earth and each of the chambers.

A complete understanding of this invention may be obtained from the following fully detailed description of a specific embodiment thereof, when read in conjunction with the appended drawing, which shows a cross sectional view of a freeze point located in the earth.

In the drawing, one form of apparatus embodying the present invention is disclosed as comprising a bore hole 12 formed in the earth 14. Located within bore hole 12 is a sealing means such as a packer 16 which functions to divide the bore hole into an upper chamber 18 and a lower chamber 20. Means, such as a conduit 22, are provided to allow communication with chamber 20 and the surface of the earth. Conduit 22 passes through and seats within an aperture 24 formed in packer 16 at its lower end while the opposite end of conduit 22 is attached through suitable coupling 26 to heat exchange means such as tubing spiral 28. The upper portion of tubing 28 is valved as at 30 and communicates with a source of lowtemperature material, not shown, or, alternatively, with the atmosphere.

Reservoir means, indicated generally by number 32, surrounds the upper portion of conduit 22 and tubing 28, and comprises a vertical cylindrical member 34 which is secured at its upper end through a flanged coupling 36 to a hopper 38. A suitable cover 40, which may be provided with a hinged lid 42, functions to allow access to the interior of hopper 38 while a quantity of thermal insulation 44 is provided around the hopper and the cover in order to minimize heat leakage into the interior of the hopper. i

If desired, an inlet conduit 46, provided with an expansion valve 48, may be prassed through a wall of hopper 38. With this type of structure it is possible to provide a relatively high pressure source (not shown) of lowtemperature material which is flashed in passing through valve 48 to form a low-temperature solid in the interior of hopper 38 and in chamber 18. A vent 50 having a valve 52 passes through the wall of cylindrical member 34 to provide communication between chamber 18 and the atmosphere or, if desired, with a recirculating system.

In practicing the present invention as it relates to the structure previously described for the purpose of forming an ice wall, a plurality of bore holes 12 is formed in the earth in a closed pattern. The spacing of these bore holes will, of course, depend on many factors such as the degree of water saturation of the earth, the depth to which the proposed excavation is to be made and the degree of natural consolidation and water permeability of the earth which is to be frozen. In general, freeze point spacing will be from about three to about seven feet with an average spacing being about five feet.

After the bore holes are formed in the desired pattern, the apparatus shown in the drawing is then located superjacent each bore hole and a source of low-temperature material is connected to tubing spiral 28 through valve 30 whereupon the material is caused to fiow through tubing 28, coupling 26, and conduit 22 into chamber of the bore hole. A supply of this material may be either constant or intermittent and in a preferred embodiment the low-temperature material is allowed to pass through chamber 20 until the chamber is substantially filled, thereupon tubing 28 is removed from communication from the source of low-temperature material by means not shown and is vented to the atmosphere to dispose of boil off arising from the vaporization of low-temperature material in chamber 20. After a sufficient period of time to allow 7 initial freezing of the soil immediately adjacent chamber 20, usually from about twenty to about one hundred twenty days, during which time the low-temperature material within the chamber is replenished as necessary, a quantity of low-temperature material having a temperature above that of the material placed within chamber 20 is dumped into hopper 38 from which it drops into chamber 18. This low-temperature material preferably is in solid form and may be furnished to hopper 38 by means of inlet 46. For instance, when a source of highpressure carbon dioxide is utilized, this material may be flashed from the vapor or liquid phase to form solid carbon dioxide in the hopper. Alternatively, the second lowtemperature material may be placed in the hopper through lid 42.

Vapors arising from the second low-temperature material in chamber 18 escape through vent 50 while those from chamber 20 pass through coil 28 and thereby remove heat from the material within the hopper.

Excavation may be begun adjacent the freeze point at such time as the earth surrounding the upper portion has frozen to a sufficient degree to allow removal of the adjacent material. This time will, of course, vary depending upon the degree of water saturation and the temperature of the material placed in chamber 18; however, in general when carbon dioxide is used for this purpose it is found that excavation may be begun in from about twenty to about to about one hundred twenty days after the initial freezing of the formation surrounding chamber 18.

A number of materials may be utilized in combination with structure shown in the drawing, the only requirement for the materials being that the material placed in the vertical lower chamber be at a lower temperature than the temperature of the material placed in the upper chamber. While low-temperature gas is not practical, it is possible to obtain advantageous results by utilizing low-temperature materials which are either in the liquid or solid phase. In a preferred embodiment, liquid nitrogen is utilized for freezing the earth which surrounds chamber 20, while solid carbon dioxide is recommended for freezing the earth surrounding chamber 18. Moreover when solids such as carbon dioxide are used, it will commonly be found advantageous to form a liquid-solid slurry with these materials to improve heat exchange across the walls of the bore hole. Thus, with carbon dioxide, acetone or trichloroethylene may be used to form a slurry.

It will be appreciated that by using the relatively lowest temperature material at the bottom of the hole it is thereby possible to obtain greater strength per horizontal unit length of ice thus formed. By this invention, a relatively uniform wall of ice can be formed which is of minimum thickness and which provides a greater strength in the more high strength portions of the earth where such greater strength is needed. Moreover, in the above description of one method for practicing the present invention, the low-temperature material was described as being placed into chamber 20 at a time prior to the initiation of freezing from chamber 18. This, however, does not represent the only manner in which the method can be practiced. More particularly, it is entirely feasible to initiate freezing from chamber 18 and thereafter to position lower-temperature material in chamber 20, or, in the alternative, to freeze simultaneously. Moreover, while there is disclosed heretofore a method and apparatus for utilizing a bore hole which is divided into two chambers, it is entirely feasible to use three or more chambers with materials of increasingly low temperature being placed from the top to the bottom of the bore hole.

Ordinarily the method and apparatus of this invention will find its primary utilization in earth construction; however, the principles involved are not restricted to earth removal but may find utilization in other applications. For instance, it has been suggested that coifer dams could be built in aqueous environments by freezing a wall of wet sand or other granular material; and, under such circumstances, the present invention would have obvious utility.

It is to be understood that the above-described arrangement is but illustrative of the appliicaton of the principles of this invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

1. The combination with a hole in water-bearing material which comprises:

(a) sealing means located in said hole at an intermediate position thereof whereby said hole is divided into an upper and a lower chamber;

(b) a conduit passing through said upper chamber and communicating with said lower chamber;

(c) a source of refrigerant communicating with said upper chamber; and

(d) a second source of refrigerant, at lower temperature than the refrigerant of paragraph (c), communicating with said lower chamber by way of said conduit.

2. The apparatus of claim 1 wherein said source of refrigerant of paragraph (c) comprises a source of highpressure carbon dioxide gas in communication with said upper chamber by way of an expansion valve.

3. The combination defined in claim 1 further characterized by a vent communicating with said upper chamber.

4. The apparatus defined in claim 3 wherein a quantity of thermal insulation is provided on said reservoir means.

5. The combination defined in claim 2 wherein said conduit is formed into a spiral within the reservoir means.

6. The method of freezing water-bearing material which comprises:

(a) forming a hole in said water-bearing material;

(b) dividing said hole into an upper and lower chamber;

(c) placing a first low-temperature material in said upper chamber;

(d) maintaining said material within said upper chamber until a portion of the water bearing material surrounding said upper chamber freezes; and

(0) either prior to, subsequent to, or simultaneously 10. The method defined in claim 9 wher with the placing of step (c), placing a quantity of is nitrogen. a second low-temperature material in said lower ein said liquid References Cited chamber, the temperature of said second material being lower than that of said first material. 5 UNITED STATES PAThNTS 7. The method defined in claim 6 wherein said first 371,389 10/1887 Sooy Smith 6136.1 material is a solid. 786,382 4/ 1905 Reno 6136.1 8. The method defined in claim 7 wherein said second 3,064,436 11/ 1962 Loofbourow 61.5 material is a liquid. 3,276,213 10/1966 Soesan 61.5 X

9. The method defined in claim 6 wherein said first material is carbon dioxide. 10 JACOB SHAPIRO, Primary Examiner. 

